Generally, a thin film is used as, for example, a dielectric film of a semiconductor device, a transparent conductor of a liquid crystal display device, a protection layer of an electroluminescent thin film display, and the like. In particular, when the thin film is used as the dielectric film of the semiconductor device, it is required to have no impurity or defect in the dielectric film and at an interface of the dielectric film to secure high capacitance and suppress current leakage. Further, a thin film must have excellent step coverage and uniformity.
However, the use of a typical chemical vapor deposition (CVD) method, a typical physical vapor deposition (PVD) method, or the like in the formation of the thin film makes it difficult to achieve excellent step coverage. In the typical CVD method, a deposition process utilizing a surface kinetic mode allows the dielectric film having relatively excellent step coverage to be obtained, but since reactants needed to deposit the dielectric film are simultaneously delivered onto a substrate, it is difficult to adjust the step coverage at a specific portion on the substrate as necessary.
Recently, in order to overcome the aforementioned problem, thin film forming methods have been proposed in which reactants are periodically supplied onto the surface of a substrate on which a thin film is to be formed, activating a surface kinetic region, resulting in generally excellent step coverage. These methods include, for example, atomic layer deposition (ALD), cyclic chemical vapor deposition (cyclic CVD), digital chemical vapor deposition (Digital CVD), and advanced chemical vapor deposition (advanced CVD).
Further, in order to introduce a thin film material, which has an excellent property in a bulk state, there is a need for a thin film forming technique capable of allowing the material to maintain its excellent property even after the thin film has been formed. However, in the case where the thin film is fabricated using the foregoing methods, unnecessary atoms contained in a chemical ligand constituting reactants remain in the thin film, and become impurities or particles on the surface of the substrate. The residues produced in the thin film forming process significantly affect the control of the impurities or particles in the thin film.
In the above-mentioned thin film forming techniques, necessary atoms, as the thin film material are delivered in a high vapor pressure state onto the substrate having the thin film formed. For this reason, even reactants such as metal organic precursors, metal halides, or the like may be delivered in a vapor state onto the substrate, in addition to the normally necessary elements. To minimize the impurities in the thin film that is desired to be formed, metal atoms and organic ligands or halides among the reactants, which are delivered onto the substrate as described above, are removed by decomposition in the chemical vapor deposition (CVD) method while they are removed by chemical displacement in the atomic layer deposition (ALD) method. That is, in the atomic layer deposition (ALD) method, necessary source gases are not mixed in a reaction chamber but are flowed into the chamber in a pulse manner one by one. For example, when a thin film consisting of an atomic layer is formed using first and second reactants, the thin film is formed by a method in which only the first reactant flows in a reaction chamber so that a first reaction gas is chemically adsorbed on a substrate, and then the second reactant is supplied to the reaction chamber so that the second reactant is chemically adsorbed on the substrate. Such a thin film forming method using the atomic layer deposition is disclosed in U.S. Pat. No. 6,620,670 entitled “PROCESS CONDITIONS AND PRECURSORS FOR ATOMIC LAYER DEPOSITION (ALD) OF Al2O3.”
FIGS. 1 to 4 illustrate a conventional method for forming a thin film on a substrate using atomic layer deposition.
First, as shown in FIG. 1, a first reactant of a compound, AXn(g), is supplied onto a semiconductor substrate 10 loaded in a chamber 12, wherein A denotes a first material constituting a thin film to be deposited, and Xn denotes a material chemically combined with the material A. The first reactant of the AXn is bubbled and supplied in a gas state to the chamber 12 via a gas line. The first supplied reactant of the AXn is chemically adsorbed to the surface of the semiconductor substrate 10.
Subsequently, as shown in FIG. 2, a purging or pumping process is conducted in the chamber to leave only the AXn(s), which has been chemically adsorbed on the semiconductor substrate. Accordingly, residues, which float in the chamber 12 or are physically adsorbed on the semiconductor substrate 10, are drained away from the chamber 12.
Next, as shown in FIG. 3, a second reactant of a compound, BYn(g), is supplied into the chamber 12, wherein B denotes a second material constituting the thin film to be deposited, and Yn denotes a material chemically combined with the material B. The second reactant of the BYn is bubbled and supplied in a gas state into the chamber 12 via a separate gas line. The second supplied reactant of the BYn is chemically adsorbed to the semiconductor substrate 10, such that the thin film of AB(s) is formed by chemical displacement.
Subsequently, as shown in FIG. 4, the purging or pumping process is conducted in the chamber to leave only the thin film of the AB(s), which has been formed on the semiconductor substrate. The residues, which float in the chamber 12 or are physically adsorbed, are drained away from the chamber. Accordingly, a single layer of the chemically adsorbed thin film, namely, a single layer of the AB(s) is formed on the semiconductor substrate 10. The processes of FIGS. 1 to 4 are repeated as one cycle a plurality of times until the thin film is formed in a desired thickness.
As described above, if the bubbled reactant is supplied, the property of the formed film varies as vapor pressure of the reactant and, therefore, the reactant must be heated for sufficient supply of the reactant. In particular, if the thin film is formed of a high dielectric material having very low vapor pressure, for example, HfO2, TiO2, Ta2O5, ZrO2, Nb2O5, CeO2, In2O3, RuO2 or IrO2, long-time heating is necessarily required. The long-time heating of the reactant makes it difficult to manage the reactant, and changes the reactant in quality. Further, it increases the supply time and removal time of the reactant, resulting in semiconductor yield reduction.